1. Field of the Invention
The invention relates to a self-propelling construction machine which has a chassis which has wheels or crawler track units.
2. Description of the Prior Art
In road construction, self-propelling construction machines of different designs are used. These machines include the known road milling machines, recyclers or stabilisers. The known road milling machines can be used to remove existing layers of road from the superstructure of the road and to restore existing road coverings with the known recyclers. The known stabilisers serve to prepare the substructure for the construction of the road. Furthermore, so-called surface miners are known as self-propelling construction machines for, for example, removing coal or stone.
The above-mentioned self-propelling construction machines have a rotating milling or cutting roller with which the material is removed.
The drive of the milling roller or cutting roller requires a relatively high motor power. If the milling roller or cutting roller comes up against particularly hard material, the power which is necessary to drive the roller can become so large that the drive motor is overloaded. In addition to the overloading of the drive motor, the problem arises that when the milling roller or cutting roller comes up against particularly hard material, the drive elements and the structure of the construction machine are overloaded by shock loading. This problem occurs, in particular, in a surface miner.
The drive motor in the known self-propelling construction machines is an internal combustion engine, in particular a diesel engine, whose engine characteristic is described by a characteristic torque/rotational speed characteristic curve. The internal combustion engine is operated with a specific rotational speed, wherein there is the risk of the internal combustion engine stalling in the case of overloading.
A first power transmission line is used to transmit the drive power from the internal combustion engine to the wheels or crawler track units, while a second power transmission line is used to transmit the drive power from the internal combustion engine to the milling roller or cutting roller. The two power transmission lines each have gear mechanism systems.
Self-propelling construction machines are known in which the gear mechanism system of the power transmission line for transmitting the drive power to the wheels has an adjustable hydrostatic gear mechanism. In order to prevent overloading of the internal combustion engine, a control device for controlling the limit load is provided for the adjustable hydrostatic gear mechanism.
EP 0 497 293 A1 describes a method for controlling the limit load of a hydrostatic drive for a construction machine. The hydrostatic drive comprises a hydraulic pump which is driven by an internal combustion engine, has an adjustable delivery volume and drives a hydraulic motor via a connected hydraulic circuit. When there is a risk of overloading of the internal combustion engine, the delivery quantity of the hydraulic pump is reduced. The control is carried out as a function of the actual rotational speed of the internal combustion engine which is measured with a rotational speed sensor on the output shaft of the engine.
Control devices for hydrostatic drives of construction machines are also known, for example, from EP 0 736 708 B1 and EP 0 558 958 B1.